Flasher circuit



Sept. 6, 1955 c. L. CRADDOCK FLASHER CIRCUIT 2 Sheets-Sheet 1 Filed May8, 1955 INVENTOR CHnnLes L. cknnnoaK BY W,% 75Q W illir fitter/Le JSept. 6, 1955 c. L. CRADDOCK FLASHER CIRCUIT 2 Sheets-Sheet 2 Filed May8, 1953 G l. m I}. 7 3 3 [w M 5 I a a w w x2 my.

INVENTOR. Cmmss L. 632.400 acz United States Patent- O FLASHER CIRCUITCharles L. Craddock, North Hollywood, Calif., assignor to MichaelResearch Company, Inc., a corporation of California Application May 8,1953, Serial No. 353,736

6 Claims. (Cl. 315-183) My invention relates generally to flashersintended to control the flashing of an electric light, and moreparticularly to such flashers that are electronically operated, asopposed to those that are mechanically operated.

It is often desirable to have a flashing light, and such lights arefrequently used for warning devices or signals, for decorative purposes,and for a multitude of other uses. However, the flashing mechanismsheretofore employed have usually relied upon mechanical devices, such asmagnetically operated vibrators, motor-driven means, or thermallyactuated mechanisms. Such prior devices have been open to the objectionthat many of them will not operate in all positions, and a number ofthem are adversely afiected by the surrounding temperature. Theseobjections have seriously limited the fields to which the flashermechanisms have been applied, and in many instances, their cost has beensuch as to prevent their use where otherwise they would be acceptable.

Electric or electronic circuits are known that provide a periodic pulse,but in general, the circuits have not been suificiently stable,particularly at low frequencies, to warrant their use where reliabilityis an important factor. Furthermore, because of the particular voltagelimitations of such circuits, their use as means for controlling lightshas been neglected. However, I have found that it is possible to use thecharacteristics and peculiarities of these circuits to advantage, andhave produced flashing lights that have a very long period ofusefulness, and operate at a very low cost per hour.

It is therefore a major object of my invention to provide an electronicflasher intended primarily to operate a light source.

Another object of my invention is to provide such a flasher that mayhave its rate of flashing controlled, either being adjusted to somepredetermined value at the time the flasher is manufactured, or madecontinuously adjustable for control in the field.

It is a further object of my invention to provide an ornamental devicemaking use of such an electronic flasher, and producing a novel andpleasing effect.

Still another object of my invention is to provide an electronic flasheradapted to operate a warning signal light, the flasher having acontrollable rate of flashing, and requiring a very small current drain.

It is a still further object of my invention to provide flasher circuitsof the above described characteristics that can be easily andinexpensively formed from readily available components, and compactlyinstalled in a very small space.

An additional object is to provide a flasher means which relies uponelectronic and electrical characteristics of its components, and has nomoving parts that may become inoperative by reason of dirt, corrosion,or theposition they occupy.

These and other objects and advantages of my invention will becomeapparent from the following description of two forms thereof, and fromthe drawings illustrating those forms in which:

iii

2,717,336 Patented Sept. 6, 1955 Figure 1 is a perspective view of anornamental device, here shown as a simulated Christmas tree, in which myelectronic flasher controls the operation of the various lights thereon;

Figure 2 is a schematic wiring diagram showing the circuit used inconnection with the lights on the tree shown in Figure 1;

Figure 3 is a perspective view of a stop sign similar to that used onhighways, and in which a flashing light is normally incorporated; and

Figure 4 is a schematic wiring diagram of the flasher control used inwarning signal lights of the type shown in Figure 3.

Description of illuminated decorative article Referring now to thedrawings, in Figure 1, I have illustrated one form of a decorativearticle, such as a simulated Christmas tree on which a series of lightsare 10- catedthat flash off and on at varying times and rates. Such adevice is very attractive and the constant flashing of the lights,without any sound, quickly secures the interest of both children andadults. It will be appreciated that the use of the flashing lightshereinafter described is not restricted to such articles, but may beincorporated in many other devices.

As indicated in Figure 1, a simulated Christmas tree 10 is mounted upona base 11 that preferably comprises a box-like member within which Imount the power supply and various control members for the device. Thetree 10 should preferably be of a type having a number of thin,thread-like or wire-like projecting members that simulate the appearanceof branches and foliage of an actual tree. Mounted on the tree, andpositioned in the general manner of the usual Christmas tree decorationsare, a plurality of bulbs 12 that flash olf and on, each bulb having itsown rate of flashing, independent of the remainder. The wires connectingthe bulbs to the power supply and control mechanism in the base 11 maybe conveniently run down the trunk of the tree 10, preferably withinthat trunk, but arranged otherwise if so desired. A switch 13 may bemounted on the base 11 to control the operation of the lamp 12, but aswill hereinafter become more apparent, in most instances this switch isnot needed. p

In Figure 2, I have indicated the schematic wiring diagram of thecontrol unit, power supply, and lamps 12, the control unit or units andthe battery being located within the base 11. As indicated in thatfigure, I provide a battery 14, preferably of dry cell type, and connectits" output terminals, through switch 13 to a pair of power leads 15 and16. t

Branching off from the power'lead 15 are conductors 17, each of whichleads to an individual lamp 12, and as indicated'by the dottedcontinuation of lead 15, the circuit may be continued to provide as manylamps 12 as are desired.

Branching off from the other power lead 16 are a series of conductors20, and individually connected to each of these conductors is an RCcircuit 21 comprising a capacitor 22 and a resistor 23 connected inparallel. The other terminal of each RC circuit 21 is connected by aconductor 24 to a corresponding lamp 12, and thus each lamp is connectedby two conductors, 17 and 24, to' its associated control unit and thepower supply. In general, the capacitors 22 and the resistors 23 haveapproximately the same value, but the individual components vary betweenthe'different RC circuits. Consequently, each individual circuit isslightly different, and thus produces a slightly different rate. offlashing. By

way of example, I have found that if the following components are used,very satisfactory results are obtained:

Voltage of battery 14 135 volts (lOO-lSO volts). Lamps 12 NE-2 neon orequivalent. Capacitor 22 .25Q.05 mfd..

Resistor 23 2.0-0.5 megohms.

The circuit comprising the battery 14, thelamp 12, and the RC circuit21'. produces the same general' result as that of a relaxationoscillator. However, an inspection of this circuit will clearly indicatethe differences, and the operation of the deviceis believed to occur inthe manner now to be described. When the switch 13 is closed, a voltagesurge appears across the conductors 17 and 24, this voltage exceedingthe breakdown voltage of the lamp 12, and consequently the latter islit. However, assoon as the discharge occurs, current flows throughresistor 23 producing a voltage drop thereacross that reduces thevoltage between the conductors 17 and 24 to a point below that necessaryto maintain the discharge within the lamp. The discharge is immediatelyextinguished, and at this instant, because of the voltage drop betweenthe terminals of the resistor 23', the capacitor 22 which is connectedto these terminals, has received a charge corresponding to this voltagedrop. Until this charge is removed, the voltage appearing on theconductor 24, with respect to the conductor 17, is insufiicient to againignite the lamp or cause the discharge therein, and the lamp thusremains unlit. However, the charge upon the capacitor 22 is quicklydissipated through. the resistor 23 until the voltage between theconductors 17 and 24 once again reaches the striking voltage of the lamp12.

When the switch 13 is first closed, all of the lamps 12 flash on,substantially in unison, but thereafter the individual diiferences inthe various RC circuits 21 cause the lamps 12 to flash at differentrates. As a result, there is a random pattern of flashing of the lights12 throughout the tree 10.

It will be appreciated that each of the lights 12 requires a very smallamount of electrical power, and the RC circuit 21 likewise absorbs avery small amount of power. As a result, the lights 12 and theirassociated control circuits 21 draw a negligible amount of power, and ithas been found in practice that if the switch 13 is kept closed,

the lights will continue to flash for a period of time approximatelyequal to that of the shelf life of the battery 14. This, it will beappreciated, amounts to several months, depending upon the constructionof the particular battery. Consequently, in order to reduce the cost ofthe complete assembly, the switch 13 may be omitted, and the deviceplaced in operation by inserting a battery within the base 11, andallowing the device to operate until the shelf life of the battery hasbeen expended.

As previously indicated, the circuit indicated in Figure 2 may beextended to include more lamps 12 with their corresponding controlcircuit 21, though it will be appreciated that if too great a number oflamps are operated by a single battery 14, the operating life of thisbattery will become somewhat less than its shelf life.

Description of warning signal all) In Figures 3 and 4, I have indicateda warning flasher In some locations, as where traific signals areinstalled, a source of power together with mechanical flashing means arereadily available. However, in many other locations, these facilitiesare not provided, and an independently powered light is of great valuein such cases. For example, as indicated in Figure 3, a stop sign 3%)may be mounted upon a post or column 31, the sign having a case orhousing of considerable depth in which a source of light and its lens32, are mounted. The control circuit and the power supply are mountedwithin the housing of the sign 20, and since the sign may be located aconsiderable distance from any regular maintenance route, it isimportant that the control circuit and the power supply be of greatreliability.

In Figure 4, I have indicated the schematic wiring di agram of such acircuit that meets the aforementioned requirements as well as others. Itwill be appreciated, of course, that the use of this Warning signallight is not restricted to permanent locations, but instead the devicemay be used on temporary installations, such as barricades duringconstruction work, and in many other places. One of the major advantagesof this particular circuit is that it does not make use of anymechanically separated electrical contacts through which current ispassing, so that there is no arcing or sparking that might cause anexplosion in the event that the surrounding atmosphere is explosive.

Briefly, my preferred circuit, as illustrated in Figure 4, includes asource of power such as a battery a timing and control circuitdesignated generally by the numeral 36, an electronic switch 37, atransformer 38, and a gaseous conduction tube, preferably mounted behindthe lens 32 of the sign 30, and designated by the numeral 40. Thebattery 35 provides the power that operates the control circuit 36, andthis circuit acts to operate or trigger the electronic switch 37 so thata pulse or current is delivered to the transformer 38 which raises thevolt-' age of that pulse to a value sutlicient to energize and light thedischarge tube 40.

Considering the circuit in greater detail, it will be noted that oneterminal of the battery 35 is connected through a switch 41 to aresistor 42 that in turn is connected through a conductor 43 to oneterminal of a capacitor 44. The other terminal of the capacitor 44 isconnected through a conductor 45 to a conductor 46 that leads to oneterminal of a resistor 47, the other terminal of that resistorbeing'connected' to the remaining terminal of the battery 35.

Connected to the conductor 43 is one terminal of a variable resistor 50,the other terminal of which is connected to one terminal of a fixedresistor 51, and the other terminal of this fixed resistor is connectedto a junction point 52. A conductor 53 connects junction point 52 toanother junction point 54, and a capacitor 55 is connected betweenjunction point 54 and conductor '43.

Thus, resistors and 51 are connected in series, and capacitor 55 isconnected in parallel with the resistor circuit, thereby providing an RCcircuit not unlike the circuit 21 shown in Figure 2.

A capacitor 56 is connected between junction point 54 and conductor 46,and junction point 52 is connected by conductor 57 to anode 60 of theelectron discharge tube or electronic switch 37. The grid or controlelectrode 61 of the tube 37 is connected through a resistor 62 to theconductor 57, and may also be connected through a capacitor 63 to theconductor 46. Finally, the cathode 64 of the tube 37 is connected to ajunction point 65, and a capacitor 66 is connected between this junctionpoint and the conductor 46.

7 As will hereinafter be described, high voltage pulses marked by asign, and in many instances, a flashing red light is used in conjunctionwith that sign to call attenappear between junction and conductor 46.and conductor 67 connectsjunction 65 to one terminal of the primaryotthe transformer 38. The other terminal of the primary of transformer 38is connected to conductor 46, and the secondary terminals of thetransformer are connected to the two terminals of the gaseous conductiontube 40, one of these conductors, if so desired, being in turn connectedto conductor 46.

When switch 41 is first closed, the first action is the charging ofcapacitor 44 through resistors 42 and 47. The resistors 42 and 47 limitthe current flowing into the capacitor 44, and produce a voltage drop sothat the voltage appearing between conductors 43 and 45 is anexponentially increasing voltage that rises rapidly at first, and thenincreases at a gradually decreasing rate. The voltage appearing betweenconductors 43 and 45 is the same as the voltage appearing betweenconductors 43 and 46, and this voltage is appliedto the control circuitand electronic switch 37, connected in series. As this voltageincreases, the voltage between the junction point 52 and the conductor46 likewise increases, since tube 37 is initially non-conducting, and nolarge current is drawn through the resistors 50 and 51. However,capacitor 56, which is connected between junction point 52 and conductor46 is being charged during this period, and when the voltage appearingbetween junction point 52 and conductor 46 reaches some critical value,the electron discharge tube 37 becomes conductive, and capacitors 44 and56 discharge through it. The discharge continues until the voltagebetween junction 52 and conductor 46 decreases to a value insuificientto continue the discharge, whereupon the tube 37 becomes non-conducting.

At this point, capacitor 44 has discharged its charge through resistors50 and 51, so that the voltage at junction 52 is less than the voltageappearing upon conductor 43, both related to conductor 46. As a result,capacitor is charged, and this charge will be dissipated by the flow ofcurrent from one terminal of that capacitor, through the resistors 50and 51 through the other terminal. This flow of current throughresistors 50 and 51 7 produces a voltage drop, and when the voltage dropoccasioned by the flow of current from capacitor 44, as well as battery35, is added to this, the potential appearing between junction point 52and conductor 46, and hence the charge on capacitor 56, will be moreslowly raised. Thus, the resistors 50 and 51 and the capacitor 55 arethe fundamental elements of the timing circuit, corresponding to theresistor 23 and capacitor 22 of the RC circuit previously shown anddescribed in connection with Figure 2. The function of capacitor 44 isto provide a supply of current that may be discharged relativelyrapidly, and in an amount greater of that capable of being provided bybattery 35. The function of capacitor 56 is similar, and its effect isto reinforce or increase the brilliance of the flash occurring ingaseous discharge tube 40 since capacitor 56 discharges directly throughthe electron discharge tube 37 while capacitor 44 discharges throughresistors 50 and 51.

The operation of electron discharge tube 37 is somewhat similar to thatof a thyratron. The control electrode or grid 61 of the tube 37 isconnected through resistor 22 to conductor 57, and this conductor islikewise connected to the anode or plate of that tube. Consequently,when the tube 37 is not conducting, no current flows through theresistor 62, neglecting for the moment the presence of capacitor 63.Thus, grid 61 and anode 60 are at the same potential, and the grid actsas the trigger electrode for the tube 37. When junction 52 reaches apredetermined value, the same voltage, which appears upon the grid 61,triggers or starts the discharge in tube 37 and current flows betweenthe anode 60 and the cathode 64, and also flows through the grid 61 andthe resistor 62. However, the presence of the resistor 62 causes avoltage drop to appear across the terminals of the resistor, so that alower voltage appears upon the grid 61 than the anode 60 when the tubeis conducting. This, however, does not stop the discharge within thetube 37 once it has been initiated.

The effect of the capacitor 63 is to receive a charge while the tube 37is not conducting, and to discharge a portion of this charge whenconduction is first established. At the time that the discharge throughthe tube ceases, the capacitor 63 can again reach itsdischarge-initiating potential, the capacitor 63 must be recharged tothis value. As a result, the presence of the capacitor 63 is to permitthe obtaining of a lower flash rate for the timing and control circuit36, without any change in the brilliance in the flash obtained.

Cathode 64 is connected in series with the primary of transformer 38,and when tube 37 is non-conducting, the potential of the cathode issubstantially equal to that of conductor 46. However, the primary of thetransformer 38, has a certain resistance, and when the first peakcurrent from the .tube 37 flows through the primary, this produces avoltage drop that causes the capacitor 66 to be charged. As the tube 37discharges, the first surge of current decreases or decays, and a lowervoltage drop appears between the terminals of the primary of transformer38. As this occurs, the capacitor 66 returns the energy stored in it, tothe circuit and the charge on the capacitor 66 is then dischargedthrough the primary of the transformer 38. This means that the lamp 40is illuminated a slightly longer time. The etfect of the capacitor 66 isthus to decrease the initial surge of current through the primary oftransformer 38, and to continue the passage of current through thatprimary for a longer period of time.

Flashing rate of the control circuit can be controlled by varyingtheresistor 50, so in this way the time to discharge capacitor 55 can becontrolled. Each of the different capacitors and resistors has its owneffect on the flash rate, some increasing and some decreasing thefrequency of flashing. Very satisfactory results will be obtained if thefollowing values of the various components are used:

Battery 35 360 volts.

Resistors 42 and 47 47,000 ohms.

Capacitor 44 2.0 mfd.

Resistor 50 500,000 ohms.

Resistor 41 47,000 ohms.

Capacitor 55' 2.0 mfd.

Capacitor 46 0.5 mfd.

Resistor 62 2.5 megohms.

Capacitor 63 0.5 mfd.

Tube 36 OA4G (cold cathode,

triode, gas-filled).

Capacitor 66 0.5 mfd.

Transformer 38 1 to ratio.

These values work very satisfactorily, and a wide range of flashingrates may be obtained. For convenience, it is sometimes desirable tocombine the variable resistor 50 with the switch 21 so that as thecontrol knob of the resistor is first turned, the first action is toclose switch 41 and thereafter the value of the resistor in the circuitmay be controlled.

As previously indicated, it is possible to omit capacitor 63 from thecircuit, and this may be particularly desirable where simplification isin order. Under these circumstances, the circuit may be furthersimplified by reducing the value of resistor 47 to zero, but when thisis done, capacitor 56 should be increased to a value of 4 mfd. In allimportant respects this simplified circuit operates in the same manneras does the more elaborate circuit, and where cost and reliability areof utmost importance, the simplified circuit produces very satisfactoryresults.

From the foregoing, it will be seen that the flasher circuit justdescribed has many advantages over the mechanically operated flashingsystems previously used. Important among these is the fact that allmoving contacts are eliminated, and consequently there is no opportunityfor corrosion, dust, or other high resistance material to interfere withthe operation of the electrical components of the circuit. Additionally,since no moving mechanical elements are concerned, the device willoperate equally well in any position, and vibration has a very minimumof effect upon it. Likewis with the elimination of open contacts andtheir sparking, the device may safely be used in an explosive orotherwise hazardous atmosphere, where heretofore previous devices werenot practical.

All of the circuits shown and described herein have made use ofconduction devices, such as the lamps 12 of the circuit shown in Figure2, having particular electrical properties. In each circuit, the lamp112 or theelectron discharge tube 37 has the characteristics ofremaining substantially non-conductive until a relatively high breakdownvoltage is applied to it, whereupon the device becomes conductive andhas a comparatively low resistance. Once the conductive state isachieved, the voltage may be reduced and the device will remainconductive until a relatively low extinction voltage is reached,whereupon the device becomes non-conductive and remains so until thebreakdown voltage is again applied. These characteristics are those of aglow discharge device, and

when I refer to such characteristics, these are the ones I means toinclude.

It will thus be seen that I have shown and described an electronicflashing circuit fully capable of achieving the objects and securing theadvantages heretofore set forth.

Many modifications and variations will occur to those skilled in theart, but these are included within the broad scope of my invention.Consequently, I do not wish to be restricted to the particular formsdescribed and shown except as limited by my claims.

I claim:

1. A flasher circuit of the class described which includes: a conductivedevice having the electrical characteristics of a glow discharge device;a control circuit comprising a resistor and a capacitor connected inparallel; a power utilization device connected in series with saidconductive device; a reinforcing capacitor connected in parallel withthe series circuit comprising said conductive device and saidutilization device, forming a first series-parallel circuit; meansconnecting said control circuit in series with said firstseries-parallel circuit to form a second seriesparallel circuit; a powercapacitor connected in parallel with said series-parallel circuit toform a network; and a resistor connected in series with said network andthrough which said network is adapted to be connected to a source ofelectrical energy.

2. A flasher circuit of the class described which includes: a conductivedevice having the electrical characteristics of a glow discharge device;a control circuit comprising a resistor and a capacitor connected inparallel; a reinforcing capacitor connected in parallel with saidconductive device; means connecting said control circuit in series withsaid parallel circuit to form a seriesparallel circuit; a powercapacitor connected in parallel with said second series-parallel circuitto form a network; and a resistor connected in series with said networkand through which said network is adapted to be connected to a source orelectrical energy.

3. A flasher circuit of the class described which includes: a conductivedevice having the electrical characteristics of a glow discharge device;a control circuit comprising a resistor and a capacitor connected inparallel; a transformer having its primary winding connected in serieswith said conductive device; a modifying capacitor connected in parallelwith said primary winding and acting to modify the pulse of currentthrough the latter; a reinforcing capacitor connected in parallel withthe circuit comprising said conductive device, said primary winding, andsaid modifying capacitor to form a first seriesparallel circuit; andmeans connecting said control circuit in series with said firstseries-parallel circuit to form a second series-parallel circuit, saidmeans being further adapted to connect said second series-parallelcircuit to a source of electrical energy.

4. A flasher circuit of the class described which in- 8 cludes: aconductive device having the electrical characteristics of a glowdischarge device; a control circuit comprising a resistor and acapacitor connected in parallel; a transformer having its primarywinding connected in series with said conductive device; a modifyingcapacitor connected in parallel with said primary winding and acting tomodify the pulse of current through the latter;

means connecting said control circuit in series with said conductivedevice and the parallel circuit formed by said primary winding and saidmodifying capacitor, to form a series parallel circuit; a powercapacitor connected in parallel with said series-parallel circuit toform a network; and a resistor connected in series with said network andthrough which said network is adapted to be connected to a source ofelectrical energy.

5. A flasher circuit of the class described which includes: a conductivedevice having the electrical char acteristics of a glow dischargedevice; a control circuit comprising a resistor and a capacitorconnected in parallel; a transformer having its primary windingconnected in series with said conductive device; a modifying capacitorconnected in parallel with said primary winding and acting to modify thepulse of current through the latter; a reinforcing capacitor connectedin parallel with the circuit comprising said conductive device, saidprimary winding, and said modifying capacitor to form a firstseries-parallel circuit; means connecting said control circuit in seriesWith said first series-parallel circuit to form a second series-parallelcircuit; a power capacitor connected in parallel with saidseries-parallel circuit to form a network; and a resistor connected inseries with said network and through which said network is adapted to beconnected to a source of electrical energy.

6. A flasher circuit of the class described which includes: an electrondischarge tube having the electrical characteristics of a glow dischargedevice, and including an anode, a cathode, and a control electrode; agaseous conduction, electrical discharge tube providing light whenenergized; a common conductor; a transformer having its secondarywinding connected to said gaseous conduction tube for operation thereof,and having one of its primary winding terminals connected to saidcathode, and the other primary winding terminal connected to said commonconductor; a modifying capacitor connected in parallel with said primarywinding; a control resistor; a control capacitor connected in parallelwith said control resistor to form a control circuit having a pair ofterminals, the first of which is connected to said anode of saidelectron discharge tube; a limiting resistor connecting said controlelectrode to said first terminal of said control circuit; a retardingcapacitor connected between said control electrode and said commonconductor; a reinforcing capacitor connected between said first terminalof said control circuit and said common conductor; a power capacitorconnected between the other terminal of said control circuit and saidcommon conductor; a resistor having one terminal connected to said otherterminal of said control circuit; and means for connecting the otherterminal of said last-mentioned resistor and said common conductor tothe terminals of a source of electrical energy.

References Cited in the file of this patent UNITED STATES PATENTS

